Variable coupling device



Filed May 22, 1936 INVENTOR F KREIENFELD BY vfq 4 ATTORNEY Patented May 31, 1938 UNITED STATES PATENT OFFICE VARIABLE COUPLING DEVICE tion of Germany Application May 22,

1936, Serial No. 81,146

In Germany July 19, 1935 2 Claims.

A gradually variable coupling can be easily obtained by arranging two coils movable towards each other. If in such an arrangement very small coupling degrees are to be attained, it is necessary to space the coils very far apart.

In modern radio amplifiers such a condition is very disadvantageous, since it is contrary to the desire to reduce the size of the amplifier structure. On the other hand, it is however desirable to provide a coupling that is variable within wide limits so as to obtain a possibly wide control range, for example, for purposes of volume control.

This invention provides means to obtain a practically complete decoupling of two coils without departing thereby from the principle of a small assembly.

According to the invention, a coil inserted in a circuit is so arranged upon, or near the other coil that it has a decoupling effect upon the field of the two coils. In many cases, the desired effect can be achieved with a single winding turn or loop (for example a lead-in wire).

For a better understanding of the invention reference is made to the accompanying drawing, in which;

Fig. 1 is a schematic circuit diagram of the input circuit of a radio receiver embodying the invention,

Fig. 2 shows an arrangement of the transformer coils according to the invention, and

Fig. 3 is a circuit diagram showing the use of a lead wire as a reverse turn coil.

In Figure 1 this variable coupling is utilized in an antenna coupling of a receiver. Numeral I designates the antenna, 2 is the antenna coil primary, 3 represents the tuned input circuit of the tube 4 with the secondary coil 5 and variable condenser 6. Numeral I designates the third coil according to the invention and which is inserted in the antenna circuit, but disposed upon, or near the coil 5. The angular direction of winding of I is so chosen that the coil produces a voltage in 5 whose phase is displaced 180 degrees from that produced by coil 2.

In Figure 2 the coil arrangement for the circuit of Figure 1 is schematically represented. 2 denotes the antenna coil, 9 the supporting arm therefor which is rotatably mounted on shaft l0, 5 represents the secondary coil, 8 is a high frequency iron core, 1 designates the auxiliary winding connected in series to the antenna coil 2 as by a lead l5 and rigidly fastened with coil 5 in the chassis.

To further elucidate the idea of the invention, Figure 3 shows the two coupling coils turned at 180 degrees to each other. This turning takes place about the shaft Hi. In this figure, 2 is again the antenna coil, 5 is the tuned circuit coil, 1 is the turn or loop formed by the earth lead of coil 2, II is the connection from the antenna to the antenna coil. As indicated in Figure 3, the coil 2 is wound in the clockwise direction. The same direction pertains also for the loop 1 connected to ground at point i2. But it should be borne in mind that the coil 2 is shown swung about the shaft ill by 180 degrees, so that in fact the winding direction of 2 is opposite to that of I.

In addition it must be pointed out that once the position of coil 1 relative to coil 5 is chosen, this position remains constant. Hence, no coupling change occurs between I and 5 upon the variation of the coupling between coils 2 and 5.

In a closely coupled state, the counter coupling produced by I is practically negligible, since the winding or turn ratio between coil 1 and coil 2 is usually less than 1/50. Thus a limitation of the control range towards high coupling degrees practically does not occur.

Having described my invention, what I claim as novel and desire to secure by Letters Patent is:

1. In combination, a radio device having a resonant input circuit comprising a transformer secondary winding having a plurality of turns, a single turn primary winding fixed with reference to said secondary winding, a second primary winding connected in series with said single turn winding and having its turns wound in the opposite direction to said single turn, means for varying the coupling between said second primary winding and said secondary winding, and a. source of radio frequency signal currents coupled to said primary windings.

2. In combination, an antenna, a transformer secondary winding, a primary winding coupled to said secondary winding, 21. lead connecting one end of said primary to said antenna, a lead connecting the other end of said primary to ground, said last named lead being formed into a loop of at least one turn which encircles said secondary winding and the voltage induced in said secondary by said loop being opposed to that induced therein by said primary winding and means for changing the degree of coupling between said primary and secondary windings.

FRIEDRICH KREIENFELD. 

